I used a DVI-D to HDMI Cable to hook up my Mac Pro to my Samsung LCD. The image looks great but had no sound. I read that I needed stereo audio cable to get sound. So I bought one and hooked it up to every known audio outlet from the Mac to every known input on the LCD and went into preferences to change the sound output options but I cannot get sound. I'm stumped. I don't know what the issue is. Do I need to upgrade a sound card?